A generic code extractor: given a list of BasicBlocks, it will rip them out into

a new function, taking care of inputs and outputs.

llvm-svn: 11935
This commit is contained in:
Misha Brukman 2004-02-28 03:26:20 +00:00
parent be74d5f73a
commit caa1a5abeb
1 changed files with 573 additions and 0 deletions

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//===- CodeExtractor.cpp - Pull code region into a new function -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the interface to tear out a code region, such as an
// individual loop or a parallel section, into a new function, replacing it with
// a call to the new function.
//
//===----------------------------------------------------------------------===//
#include "llvm/BasicBlock.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/FunctionUtils.h"
#include "Support/Debug.h"
#include "Support/StringExtras.h"
#include <algorithm>
#include <map>
#include <vector>
using namespace llvm;
namespace {
inline bool contains(const std::vector<BasicBlock*> &V, const BasicBlock *BB){
return std::find(V.begin(), V.end(), BB) != V.end();
}
/// getFunctionArg - Return a pointer to F's ARGNOth argument.
///
Argument *getFunctionArg(Function *F, unsigned argno) {
Function::aiterator ai = F->abegin();
while (argno) { ++ai; --argno; }
return &*ai;
}
struct CodeExtractor {
typedef std::vector<Value*> Values;
typedef std::vector<std::pair<unsigned, unsigned> > PhiValChangesTy;
typedef std::map<PHINode*, PhiValChangesTy> PhiVal2ArgTy;
PhiVal2ArgTy PhiVal2Arg;
public:
Function *ExtractCodeRegion(const std::vector<BasicBlock*> &code);
private:
void findInputsOutputs(const std::vector<BasicBlock*> &code,
Values &inputs,
Values &outputs,
BasicBlock *newHeader,
BasicBlock *newRootNode);
void processPhiNodeInputs(PHINode *Phi,
const std::vector<BasicBlock*> &code,
Values &inputs,
BasicBlock *newHeader,
BasicBlock *newRootNode);
void rewritePhiNodes(Function *F, BasicBlock *newFuncRoot);
Function *constructFunction(const Values &inputs,
const Values &outputs,
BasicBlock *newRootNode, BasicBlock *newHeader,
const std::vector<BasicBlock*> &code,
Function *oldFunction, Module *M);
void moveCodeToFunction(const std::vector<BasicBlock*> &code,
Function *newFunction);
void emitCallAndSwitchStatement(Function *newFunction,
BasicBlock *newHeader,
const std::vector<BasicBlock*> &code,
Values &inputs,
Values &outputs);
};
}
void CodeExtractor::processPhiNodeInputs(PHINode *Phi,
const std::vector<BasicBlock*> &code,
Values &inputs,
BasicBlock *codeReplacer,
BasicBlock *newFuncRoot)
{
// Separate incoming values and BasicBlocks as internal/external. We ignore
// the case where both the value and BasicBlock are internal, because we don't
// need to do a thing.
std::vector<unsigned> EValEBB;
std::vector<unsigned> EValIBB;
std::vector<unsigned> IValEBB;
for (unsigned i = 0, e = Phi->getNumIncomingValues(); i != e; ++i) {
Value *phiVal = Phi->getIncomingValue(i);
if (Instruction *Inst = dyn_cast<Instruction>(phiVal)) {
if (contains(code, Inst->getParent())) {
if (!contains(code, Phi->getIncomingBlock(i)))
IValEBB.push_back(i);
} else {
if (contains(code, Phi->getIncomingBlock(i)))
EValIBB.push_back(i);
else
EValEBB.push_back(i);
}
} else if (Constant *Const = dyn_cast<Constant>(phiVal)) {
// Constants are internal, but considered `external' if they are coming
// from an external block.
if (!contains(code, Phi->getIncomingBlock(i)))
EValEBB.push_back(i);
} else if (Argument *Arg = dyn_cast<Argument>(phiVal)) {
// arguments are external
if (contains(code, Phi->getIncomingBlock(i)))
EValIBB.push_back(i);
else
EValEBB.push_back(i);
} else {
phiVal->dump();
assert(0 && "Unhandled input in a Phi node");
}
}
// Both value and block are external. Need to group all of
// these, have an external phi, pass the result as an
// argument, and have THIS phi use that result.
if (EValEBB.size() > 0) {
if (EValEBB.size() == 1) {
// Now if it's coming from the newFuncRoot, it's that funky input
unsigned phiIdx = EValEBB[0];
if (!dyn_cast<Constant>(Phi->getIncomingValue(phiIdx)))
{
PhiVal2Arg[Phi].push_back(std::make_pair(phiIdx, inputs.size()));
// We can just pass this value in as argument
inputs.push_back(Phi->getIncomingValue(phiIdx));
}
Phi->setIncomingBlock(phiIdx, newFuncRoot);
} else {
PHINode *externalPhi = new PHINode(Phi->getType(), "extPhi");
codeReplacer->getInstList().insert(codeReplacer->begin(), externalPhi);
for (std::vector<unsigned>::iterator i = EValEBB.begin(),
e = EValEBB.end(); i != e; ++i)
{
externalPhi->addIncoming(Phi->getIncomingValue(*i),
Phi->getIncomingBlock(*i));
// We make these values invalid instead of deleting them because that
// would shift the indices of other values... The fixPhiNodes should
// clean these phi nodes up later.
Phi->setIncomingValue(*i, 0);
Phi->setIncomingBlock(*i, 0);
}
PhiVal2Arg[Phi].push_back(std::make_pair(Phi->getNumIncomingValues(),
inputs.size()));
// We can just pass this value in as argument
inputs.push_back(externalPhi);
}
}
// When the value is external, but block internal...
// just pass it in as argument, no change to phi node
for (std::vector<unsigned>::iterator i = EValIBB.begin(),
e = EValIBB.end(); i != e; ++i)
{
// rewrite the phi input node to be an argument
PhiVal2Arg[Phi].push_back(std::make_pair(*i, inputs.size()));
inputs.push_back(Phi->getIncomingValue(*i));
}
// Value internal, block external
// this can happen if we are extracting a part of a loop
for (std::vector<unsigned>::iterator i = IValEBB.begin(),
e = IValEBB.end(); i != e; ++i)
{
assert(0 && "Cannot (YET) handle internal values via external blocks");
}
}
void CodeExtractor::findInputsOutputs(const std::vector<BasicBlock*> &code,
Values &inputs,
Values &outputs,
BasicBlock *newHeader,
BasicBlock *newRootNode)
{
for (std::vector<BasicBlock*>::const_iterator ci = code.begin(),
ce = code.end(); ci != ce; ++ci) {
BasicBlock *BB = *ci;
for (BasicBlock::iterator BBi = BB->begin(), BBe = BB->end();
BBi != BBe; ++BBi) {
// If a use is defined outside the region, it's an input.
// If a def is used outside the region, it's an output.
if (Instruction *I = dyn_cast<Instruction>(&*BBi)) {
// If it's a phi node
if (PHINode *Phi = dyn_cast<PHINode>(I)) {
processPhiNodeInputs(Phi, code, inputs, newHeader, newRootNode);
} else {
// All other instructions go through the generic input finder
// Loop over the operands of each instruction (inputs)
for (User::op_iterator op = I->op_begin(), opE = I->op_end();
op != opE; ++op) {
if (Instruction *opI = dyn_cast<Instruction>(op->get())) {
// Check if definition of this operand is within the loop
if (!contains(code, opI->getParent())) {
// add this operand to the inputs
inputs.push_back(opI);
}
}
}
}
// Consider uses of this instruction (outputs)
for (Value::use_iterator use = I->use_begin(), useE = I->use_end();
use != useE; ++use) {
if (Instruction* inst = dyn_cast<Instruction>(*use)) {
if (!contains(code, inst->getParent())) {
// add this op to the outputs
outputs.push_back(I);
}
}
}
} /* if */
} /* for: insts */
} /* for: basic blocks */
}
void CodeExtractor::rewritePhiNodes(Function *F,
BasicBlock *newFuncRoot) {
// Write any changes that were saved before: use function arguments as inputs
for (PhiVal2ArgTy::iterator i = PhiVal2Arg.begin(), e = PhiVal2Arg.end();
i != e; ++i)
{
PHINode *phi = (*i).first;
PhiValChangesTy &values = (*i).second;
for (unsigned cIdx = 0, ce = values.size(); cIdx != ce; ++cIdx)
{
unsigned phiValueIdx = values[cIdx].first, argNum = values[cIdx].second;
if (phiValueIdx < phi->getNumIncomingValues())
phi->setIncomingValue(phiValueIdx, getFunctionArg(F, argNum));
else
phi->addIncoming(getFunctionArg(F, argNum), newFuncRoot);
}
}
// Delete any invalid Phi node inputs that were marked as NULL previously
for (PhiVal2ArgTy::iterator i = PhiVal2Arg.begin(), e = PhiVal2Arg.end();
i != e; ++i)
{
PHINode *phi = (*i).first;
for (unsigned idx = 0, end = phi->getNumIncomingValues(); idx != end; ++idx)
{
if (phi->getIncomingValue(idx) == 0 && phi->getIncomingBlock(idx) == 0) {
phi->removeIncomingValue(idx);
--idx;
--end;
}
}
}
// We are done with the saved values
PhiVal2Arg.clear();
}
/// constructFunction - make a function based on inputs and outputs, as follows:
/// f(in0, ..., inN, out0, ..., outN)
///
Function *CodeExtractor::constructFunction(const Values &inputs,
const Values &outputs,
BasicBlock *newRootNode,
BasicBlock *newHeader,
const std::vector<BasicBlock*> &code,
Function *oldFunction, Module *M) {
DEBUG(std::cerr << "inputs: " << inputs.size() << "\n");
DEBUG(std::cerr << "outputs: " << outputs.size() << "\n");
BasicBlock *header = code[0];
// This function returns unsigned, outputs will go back by reference.
Type *retTy = Type::UShortTy;
std::vector<const Type*> paramTy;
// Add the types of the input values to the function's argument list
for (Values::const_iterator i = inputs.begin(),
e = inputs.end(); i != e; ++i) {
const Value *value = *i;
DEBUG(std::cerr << "value used in func: " << value << "\n");
paramTy.push_back(value->getType());
}
// Add the types of the output values to the function's argument list, but
// make them pointer types for scalars
for (Values::const_iterator i = outputs.begin(),
e = outputs.end(); i != e; ++i) {
const Value *value = *i;
DEBUG(std::cerr << "instr used in func: " << value << "\n");
const Type *valueType = value->getType();
// Convert scalar types into a pointer of that type
if (valueType->isPrimitiveType()) {
valueType = PointerType::get(valueType);
}
paramTy.push_back(valueType);
}
DEBUG(std::cerr << "Function type: " << retTy << " f(");
for (std::vector<const Type*>::iterator i = paramTy.begin(),
e = paramTy.end(); i != e; ++i)
DEBUG(std::cerr << (*i) << ", ");
DEBUG(std::cerr << ")\n");
const FunctionType *funcType = FunctionType::get(retTy, paramTy, false);
// Create the new function
Function *newFunction = new Function(funcType,
GlobalValue::InternalLinkage,
oldFunction->getName() + "_code", M);
newFunction->getBasicBlockList().push_back(newRootNode);
for (unsigned i = 0, e = inputs.size(); i != e; ++i) {
std::vector<User*> Users(inputs[i]->use_begin(), inputs[i]->use_end());
for (std::vector<User*>::iterator use = Users.begin(), useE = Users.end();
use != useE; ++use) {
if (Instruction* inst = dyn_cast<Instruction>(*use)) {
if (contains(code, inst->getParent())) {
inst->replaceUsesOfWith(inputs[i], getFunctionArg(newFunction, i));
}
}
}
}
// Rewrite branches to basic blocks outside of the loop to new dummy blocks
// within the new function. This must be done before we lose track of which
// blocks were originally in the code region.
std::vector<User*> Users(header->use_begin(), header->use_end());
for (std::vector<User*>::iterator i = Users.begin(), e = Users.end();
i != e; ++i) {
if (BranchInst *inst = dyn_cast<BranchInst>(*i)) {
BasicBlock *BB = inst->getParent();
if (!contains(code, BB) && BB->getParent() == oldFunction) {
// The BasicBlock which contains the branch is not in the region
// modify the branch target to a new block
inst->replaceUsesOfWith(header, newHeader);
}
}
}
return newFunction;
}
void CodeExtractor::moveCodeToFunction(const std::vector<BasicBlock*> &code,
Function *newFunction)
{
for (std::vector<BasicBlock*>::const_iterator i = code.begin(), e =code.end();
i != e; ++i) {
BasicBlock *BB = *i;
Function *oldFunc = BB->getParent();
Function::BasicBlockListType &oldBlocks = oldFunc->getBasicBlockList();
// Delete the basic block from the old function, and the list of blocks
oldBlocks.remove(BB);
// Insert this basic block into the new function
Function::BasicBlockListType &newBlocks = newFunction->getBasicBlockList();
newBlocks.push_back(BB);
}
}
void
CodeExtractor::emitCallAndSwitchStatement(Function *newFunction,
BasicBlock *codeReplacer,
const std::vector<BasicBlock*> &code,
Values &inputs,
Values &outputs)
{
// Emit a call to the new function, passing allocated memory for outputs and
// just plain inputs for non-scalars
std::vector<Value*> params;
BasicBlock *codeReplacerTail = new BasicBlock("codeReplTail",
codeReplacer->getParent());
for (Values::const_iterator i = inputs.begin(),
e = inputs.end(); i != e; ++i)
params.push_back(*i);
for (Values::const_iterator i = outputs.begin(),
e = outputs.end(); i != e; ++i) {
// Create allocas for scalar outputs
if ((*i)->getType()->isPrimitiveType()) {
Constant *one = ConstantUInt::get(Type::UIntTy, 1);
AllocaInst *alloca = new AllocaInst((*i)->getType(), one);
codeReplacer->getInstList().push_back(alloca);
params.push_back(alloca);
LoadInst *load = new LoadInst(alloca, "alloca");
codeReplacerTail->getInstList().push_back(load);
std::vector<User*> Users((*i)->use_begin(), (*i)->use_end());
for (std::vector<User*>::iterator use = Users.begin(), useE =Users.end();
use != useE; ++use) {
if (Instruction* inst = dyn_cast<Instruction>(*use)) {
if (!contains(code, inst->getParent())) {
inst->replaceUsesOfWith(*i, load);
}
}
}
} else {
params.push_back(*i);
}
}
CallInst *call = new CallInst(newFunction, params, "targetBlock");
codeReplacer->getInstList().push_back(call);
codeReplacer->getInstList().push_back(new BranchInst(codeReplacerTail));
// Now we can emit a switch statement using the call as a value.
// FIXME: perhaps instead of default being self BB, it should be a second
// dummy block which asserts that the value is not within the range...?
//BasicBlock *defaultBlock = new BasicBlock("defaultBlock", oldF);
//insert abort() ?
//defaultBlock->getInstList().push_back(new BranchInst(codeReplacer));
SwitchInst *switchInst = new SwitchInst(call, codeReplacerTail,
codeReplacerTail);
// Since there may be multiple exits from the original region, make the new
// function return an unsigned, switch on that number
unsigned switchVal = 0;
for (std::vector<BasicBlock*>::const_iterator i =code.begin(), e = code.end();
i != e; ++i) {
BasicBlock *BB = *i;
// rewrite the terminator of the original BasicBlock
Instruction *term = BB->getTerminator();
if (BranchInst *brInst = dyn_cast<BranchInst>(term)) {
// Restore values just before we exit
// FIXME: Use a GetElementPtr to bunch the outputs in a struct
for (unsigned outIdx = 0, outE = outputs.size(); outIdx != outE; ++outIdx)
{
new StoreInst(outputs[outIdx],
getFunctionArg(newFunction, outIdx),
brInst);
}
// Rewrite branches into exists which return a value based on which
// exit we take from this function
if (brInst->isUnconditional()) {
if (!contains(code, brInst->getSuccessor(0))) {
ConstantUInt *brVal = ConstantUInt::get(Type::UShortTy, switchVal);
ReturnInst *newRet = new ReturnInst(brVal);
// add a new target to the switch
switchInst->addCase(brVal, brInst->getSuccessor(0));
++switchVal;
// rewrite the branch with a return
BasicBlock::iterator ii(brInst);
ReplaceInstWithInst(BB->getInstList(), ii, newRet);
delete brInst;
}
} else {
// Replace the conditional branch to branch
// to two new blocks, each of which returns a different code.
for (unsigned idx = 0; idx < 2; ++idx) {
BasicBlock *oldTarget = brInst->getSuccessor(idx);
if (!contains(code, oldTarget)) {
// add a new basic block which returns the appropriate value
BasicBlock *newTarget = new BasicBlock("newTarget", newFunction);
ConstantUInt *brVal = ConstantUInt::get(Type::UShortTy, switchVal);
ReturnInst *newRet = new ReturnInst(brVal);
newTarget->getInstList().push_back(newRet);
// rewrite the original branch instruction with this new target
brInst->setSuccessor(idx, newTarget);
// the switch statement knows what to do with this value
switchInst->addCase(brVal, oldTarget);
++switchVal;
}
}
}
} else if (ReturnInst *retTerm = dyn_cast<ReturnInst>(term)) {
assert(0 && "Cannot handle return instructions just yet.");
// FIXME: what if the terminator is a return!??!
// Need to rewrite: add new basic block, move the return there
// treat the original as an unconditional branch to that basicblock
} else if (SwitchInst *swTerm = dyn_cast<SwitchInst>(term)) {
assert(0 && "Cannot handle switch instructions just yet.");
} else if (InvokeInst *invInst = dyn_cast<InvokeInst>(term)) {
assert(0 && "Cannot handle invoke instructions just yet.");
} else {
assert(0 && "Unrecognized terminator, or badly-formed BasicBlock.");
}
}
}
/// ExtractRegion - Removes a loop from a function, replaces it with a call to
/// new function. Returns pointer to the new function.
///
/// algorithm:
///
/// find inputs and outputs for the region
///
/// for inputs: add to function as args, map input instr* to arg#
/// for outputs: add allocas for scalars,
/// add to func as args, map output instr* to arg#
///
/// rewrite func to use argument #s instead of instr*
///
/// for each scalar output in the function: at every exit, store intermediate
/// computed result back into memory.
///
Function *CodeExtractor::ExtractCodeRegion(const std::vector<BasicBlock*> &code)
{
// 1) Find inputs, outputs
// 2) Construct new function
// * Add allocas for defs, pass as args by reference
// * Pass in uses as args
// 3) Move code region, add call instr to func
//
Values inputs, outputs;
// Assumption: this is a single-entry code region, and the header is the first
// block in the region. FIXME: is this true for a list of blocks from a
// natural function?
BasicBlock *header = code[0];
Function *oldFunction = header->getParent();
Module *module = oldFunction->getParent();
// This takes place of the original loop
BasicBlock *codeReplacer = new BasicBlock("codeRepl", oldFunction);
// The new function needs a root node because other nodes can branch to the
// head of the loop, and the root cannot have predecessors
BasicBlock *newFuncRoot = new BasicBlock("newFuncRoot");
newFuncRoot->getInstList().push_back(new BranchInst(header));
// Find inputs to, outputs from the code region
//
// If one of the inputs is coming from a different basic block and it's in a
// phi node, we need to rewrite the phi node:
//
// * All the inputs which involve basic blocks OUTSIDE of this region go into
// a NEW phi node that takes care of finding which value really came in.
// The result of this phi is passed to the function as an argument.
//
// * All the other phi values stay.
//
// FIXME: PHI nodes' incoming blocks aren't being rewritten to accomodate for
// blocks moving to a new function.
// SOLUTION: move Phi nodes out of the loop header into the codeReplacer, pass
// the values as parameters to the function
findInputsOutputs(code, inputs, outputs, codeReplacer, newFuncRoot);
// Step 2: Construct new function based on inputs/outputs,
// Add allocas for all defs
Function *newFunction = constructFunction(inputs, outputs, newFuncRoot,
codeReplacer, code,
oldFunction, module);
rewritePhiNodes(newFunction, newFuncRoot);
emitCallAndSwitchStatement(newFunction, codeReplacer, code, inputs, outputs);
moveCodeToFunction(code, newFunction);
return newFunction;
}
Function* llvm::ExtractLoop(Loop *L) {
CodeExtractor CE;
return CE.ExtractCodeRegion(L->getBlocks());
}